The present invention relates generally to ink-jet printing and, more particularly, to a technique for printing a bar code while conserving colorant during bar code printing operations.
Modern printing devices utilize an ink ejecting printhead that is often mounted in a carriage that is moved back and forth across print media, such as paper for example. As the printhead moves across the print media, a control system activates the printhead to deposit or eject ink droplets, or colorants, onto the print media to form images and text.
The printhead is sometimes fluidly coupled to an ink container that supplies ink to the printhead. The container may be a multi-chamber ink container that contains more than one colorant. Such containers typically contain one or more, of the following colorants: black, cyan, yellow and magenta. Each chamber of the multi-chamber ink container is fluidly coupled to the printhead.
A shortcoming of the multi-chamber ink container is that when any of the ink chambers of the container is depleted of ink, the entire ink container must be replaced, since the printing device is no longer capable of full color printing. Of course, discarding the entire multi-chamber container prevents the remaining colorants from being used, thereby causing waste. Thus, colorant management and conservation are important considerations in ink-jet printing operations.
A significant challenge to colorant management and conservation is presented in bar code printing. It is understood that a bar code is a code consisting of ink lines of varying widths that can be read optically with a scanning device to convert data represented by the bar code into digital signals. In many cases the bar codes are printed in monochrome and black is the colorant of choice.
Since modern ink-jet printers are equipped with printheads or containers having the four above-mentioned colorants, conventional methods of printing bar codes present shortcomings in both colorant management and conservation. In such cases, the printhead for black is actively utilized while the other printheads are relatively dormant. This is not a satisfactory condition because, in order to prevent the colorant from drying in the cyan, yellow and magenta printheads, it becomes necessary to interrupt a print process that usually entails spitting cyan, magenta and yellow colorant droplets into a spittoon during the print cycle. Each such spitting event entails waste of colorant inks. Nevertheless, in order to prevent loss of an entire printhead through the drying effect, conventional systems settle for less waste through the servicing technique.
Not only is the interruption of the print cycle to service the printheads wasteful, printhead servicing during the print cycle slows throughput. In addition, such servicing may effect adversely print quality. In summary, printhead servicing during bar code printing is a wasteful practice that reduces throughput and tends to diminish print quality.
From the foregoing it will be apparent that there is a need for a technique for printing bar codes wherein colorant waste is reduced. Desirably such a technique would afford improved throughput while affording good print quality.
The various bars of a bar code convey information according to the width of the individual bars. In this regard, in order for a bar code reader to operate, the reader must be able to xe2x80x9creadxe2x80x9d the widths of the individual bars. If each bar of the code is regarded as having a leading edge and a trailing edge, each parallel to the long axis of the bar, the bar code reader can read a bar by measuring the distance between the leading edge and the trailing edge.
According to the present invention, there is provided a technique of forming a bar of a bar code on print media by a printing device having a plurality of colorants. Each one of the individual bars has a leading edge and a trailing edge that help to define a central region of the bar. The relative locations of the leading edge and trailing edge are determined and a first colorant, usually black, is deposited at the leading edge. A composite of the first colorant, and the other printhead colorants, are deposited in the central region while the first colorant is deposited at the trailing edge. A bar of a bar code produced by this technique has a clearly defined leading and trailing edge for bar code readers to measure while the central region of the bar includes a composite of colorants.
The technique of the present invention, and the bar code bar produced by the process, afford several advantages. While the leading and trailing edges enable efficient bar code readings, the central region of the bar serves to receive a composite of the colorants. In this manner, the black colorant is conserved since it no longer necessary for it to fill the entire bar and the firing duty cycle for the black printhead is reduced by about 25%. The other colorants are conserved since the need for servicing the printhead by spitting ink at a service station is eliminated. As a result, throughput and print quality are enhanced because servicing trips to the service station are eliminated as composites of colorants are deposited in the central region of the bar rather than spitting ink at the service station.
In addition, the use of composite black colorant in the middle of the bar code does not impact scannability since the process is not random, on the fly spitting but is, instead, a directed process. Moreover, since the frequency of printhead nozzle servicing is reduced, throughput is increased. The novel technique of the present invention is applicable to any image or symbol intended to be scanned by a laser or optical scanner. It is especially useful in modern tag and label printers utilizing 1 inch swath printheads at 1-pass printing.
While the invention discussed herein relates to a technique for printing bar codes, it will be apparent to those skilled in the art that the technique is suitable also for any image or symbol that is intended to be printed or scanned with a laser or optical scanner.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.